This invention relates in general to the manufacture of structural members having desired shapes, such as components for use in vehicle frame assemblies. More specifically, this invention relates to an improved apparatus and method for initially performing a heat treatment process on a closed channel structural member to facilitate the subsequent performance of a magnetic pulse welding process so as to manufacture a vehicle frame component or a portion of a vehicle frame assembly.
Many land vehicles in common use, such as automobiles, vans, and trucks, include a body and frame assembly that is supported upon a plurality of ground-engaging wheels by a resilient suspension system. The structures of known body and frame assemblies can be divided into two general categories, namely, separate and unitized. In a typical separate body and frame assembly, the structural components of the body portion and the frame portion are separate and independent from one another. When assembled, the frame portion of the assembly is resiliently supported upon the vehicle wheels by the suspension system and serves as a platform upon which the body portion of the assembly and other components of the vehicle can be mounted. Separate body and frame assemblies of this general type are found in most older vehicles, but remain in common use today for many relatively large or specialized use modem vehicles, such as large vans, sport utility vehicles, and trucks. In a typical unitized body and frame assembly, the structural components of the body portion and the frame portion are combined into an integral unit that is resiliently supported upon the vehicle wheels by the suspension system. Unitized body and frame assemblies of this general type are found in many relatively small modem vehicles, such as automobiles and minivans.
Traditionally, the various components of known vehicle body and frame assemblies have been formed from open channel structural members, i.e., structural members that have a non-continuous cross sectional shape (U-shaped or C-shaped channel members, for example). Thus, it is known to use one or more open channel structural members to form the side rails, the cross members, and other components of a vehicle body and frame assembly. However, the use of open channel structural members to form the various components of a vehicle body and frame assemblies has been found to be undesirable for several reasons. First, it is relatively time consuming and expensive to bend portions of such components to conform to a desired final shape, as is commonly necessary. Second, after such bending has been performed, a relatively large number of brackets or other mounting devices must usually be secured to some or all of such components to facilitate the attachment of the various parts of the vehicle to the body and frame assembly. Third, in some instances, it has been found difficult to maintain dimensional stability throughout the length of such components, particularly when two or more components are welded or otherwise secured together.
To address this, it has been proposed to form one or more of the various vehicle body and frame components from closed channel structural members, i.e., structural members that have a continuous cross sectional shape (tubular or box-shaped channel members, for example). This cross sectional shape is advantageous because it provides strength and rigidity to the vehicle body and frame component. Also, this cross sectional shape is desirable because it provides vertically and horizontally oriented side surfaces that facilitate the attachment of brackets and mounts used to support the various parts of the vehicle to the body and frame assembly. In some instances, the various parts of the vehicle may be directly attached to the vertically and horizontally oriented side surfaces of the vehicle body and frame assembly.
In vehicle body and frame assemblies of the type described above, it is often necessary to join two or more structural members together to form a vehicle frame component or to form a portion of the vehicle frame assembly. Traditionally, conventional welding techniques have been used to permanently join the various components of the vehicle frame together. As is well known, conventional welding techniques involve the application of heat to localized areas of two metallic members, which results in a coalescence of the two metallic members. Such welding may or may not be performed with the application of pressure, and may or may not include the use of a filler metal. Although conventional welding techniques have functioned satisfactorily in the past, there are some drawbacks to the use thereof in joining metallic vehicle frame components together. First, as noted above, conventional welding techniques involve the application of heat to localized areas of the two metallic frame members. This application of heat can cause undesirable distortions and weaknesses to be introduced into the metallic components. Second, while conventional welding techniques are well suited for joining components which are formed from similar metallic materials, it has been found to be somewhat more difficult to adapt them for use in joining components formed from dissimilar metallic materials. Third, conventional welding techniques are not easily adapted for joining components which have different gauge thicknesses. Inasmuch as the production of vehicle frames is usually an high volume, low margin process, it would be desirable to provide an improved method and apparatus for permanently joining two or more metallic vehicle frame components which avoids the drawbacks of conventional welding techniques.
This invention relates to an improved apparatus and method for initially performing a heat treatment process on a closed channel structural member to facilitate the subsequent performance of a magnetic pulse welding process so as to manufacture a vehicle frame component or a portion of a vehicle frame assembly. Initially, a workpiece is provided that is preferably formed from a closed channel structural member having a circular or box-shaped cross sectional shape. The workpiece is subjected to a scanning heat treatment process, wherein the workpiece is heat treated in a continuous and longitudinal manner from one end to the other. Preferably, the workpiece is supported vertically during the scanning heat treatment process to prevent the shape thereof from becoming distorted. The scanning heat treatment process is preferably a retrogression heat treatment process, wherein the workpiece is rapidly heated to a sufficient temperature that provides for full or partial softening thereof, followed by relatively rapid cooling. In a third step of the method, a deforming process is performed on the workpiece during the period of time following the retrogression heat treatment process in which the workpiece retains the full or partial softening characteristics. In a fourth step of the method, a magnetic pulse welding operation is performed to secure two workpieces together so as to manufacture a vehicle frame component or a portion of a vehicle frame assembly. At least one of the two workpieces is subjected to the scanning heat treatment process to facilitate the magnetic pulse welding process.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings.